A MEMS device (micro-electro-mechanical system) is a miniaturized device which integrates mechanical and electrical functions in a chip or die of semiconductor material, for example of silicon. MEMS devices offer many advantages including miniaturization, and low manufacturing costs. These advantages are realized using micro-manufacturing lithographic techniques. The final assembled device is typically made of the silicon die wherein the MEMS device is integrated and, optionally, of integrated circuits for specific applications mounted on a substrate using conventional assembling processes.
A cover or cap, fixed to the substrate is typically formed by overmolding the MEMS device and any other devices mounted on the substrate, forming a casing which protects the MEMS device against external physical stresses.
Many types of sensors can be produced in a MEMS platform. One such sensor is a microphone. Many applications incorporate MEMS microphones including cellular telephones, laptops, etc. The attraction of MEMS microphones is the ability to provide a lightweight and small form factor microphone. Because of the low manufacturing costs and small footprint, MEMS microphones are increasingly replacing electric condenser microphones (ECMs). Additionally, a MEMS microphone has an inherent advantage of low power consumption (160 μA), which is approximately ⅓ of that of the ECM. For mobile phone and laptop applications with limited power storing capacity, the power savings available using MEMS microphones is significant.
One limitation of known MEMS microphones, however, is their susceptibility to damage from moisture. For example, in order to function properly, the sensor portion of the MEMS microphone must be configured to react to sound waves. By providing access for sound waves, however, an access is also provided for moisture.
What is needed, therefore, is MEMS microphone which provides protection to the sensor area against moisture. A need also exists for a MEMS microphone which provides a defined front volume that is compatible with epoxy overmold processes such as are common to standard semiconductor packages